Click on the Database
Manager link 
in the Site Management area.
Click on the
delete icon 
next to the specific database.
Removing a database will delete that database from it's online location. Be sure that you have saved a copy of the database if you want to keep any of the information in the database. Removing a database will not remove any user's but it will remove all user's permissions to that database.
To remove a database:
Click on the Database
Manager link in the Site Management area.
Click on the
delete icon next to the specific database.